Process for preparing silver halide emulsions comprising the addition of excess chloride ion

ABSTRACT

RADIATION-SENSITIVE EMULSIONS AND ELEMENTS PARTICULARLY SUITABLE FOR USE IN HIGH INTENSITY OSCILLOGRAPHS ARE PREPARED BY ADDING TO A COLLOID-SILVER HALIDE EMULSION OF THE DEVELOPING-OUT TYPE OR DIRECT-WRITING TYPE, A LARGE AMOUNT OF A WATER SOLUBLE CHLORIDE SALT OF THE ORDER OF ABOUT 160 MOLE PERCENT BASED ON THE SILVER HALIDES AFTER DIGESTION AND PRIOR TO COATING THE EMULSION ON A SUPPORT.

United States Patent 3,597,209 PROCESS FOR PREPARING SILVER HALIDE EMULSIONS COMPRISING THE ADDITION OF EXCESS CHLORIDE ION Robert Chapman Countryman, Pittsford, N.Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. N Drawing. Filed Jan. 25, 1968, Ser. No. 700,358 Int. Cl. G03c 1/02, 1/28 US. Cl. 9694 8 Claims ABSTRACT OF THE DISCLOSURE Radiation-sensitive emulsions and elements particularly suitable for use in high intensity oscillographs are prepared by adding to a colloid-silver halide emulsion of the developing-out type or direct-writing type, a large amount of a water soluble chloride salt of the order of about 160 mole percent based on the silver halides after digestion and prior to coating the emulsion on a support.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to radiation-sensitive photographic elements comprising colloid-silver halide emulsion layers for oscillographic recording purposes having improved development and sensitometric characteristics. The present invention constitutes an improvement in the wetdevelopment response of both developing-out and photodevelopable direct writing radiation-sensitive elements which are exposed in high-intensity oscillographic recording instruments. This improvement is brought about by adding after digestion and prior to coating based on the silver halide, from 80 to- 240 mole percent and preferably 130 to 170 mole percent of a water-soluble chloride salt. The addition of a large amount of chloride ions prior to coating produces an improved wet-development response by minimizing the desensitization effect of the ambient flare light to subsequent imaging exposure. This produces higher effective sensitivity to oscillographic traces and timing lines in the high-intensity oscillographic recording instruments in use today. The addition of large amounts of chloride ions prior to coating also produces many other advantages, especially in direct-writing radiation-sensitive elements which are photodevelopable.

Description of the prior art The addition of halide ions (chloride, bromide and iodide) to photographic gelatino-silver halide emulsions is known. Further it is known to add at least 50% to 100% or more of excess bromide ions based on the silver halide to direct writing emulsions to decrease the background density. Light-developable, direct writing oscillographic recording papers are described in US. Pats. 3,033,678; 3,033,682; 3,178,293; 3,183,088; 3,189,456; 3,249,440 and others. In these patents there are described layers and processes of manufacture which provide radiation sensitive elements for recording the high intensity light traces from oscillographic recording instruments. Such elements require no chemical processing and are developed by exposure to a source of radiation of lower intensity than the image forming, high intensity source.

Emulsions for the direct-writing elements of the above patents are made by precipitating silver halides in a macromolecular colloid, e.g., gelatin, coagulating, washing the coagulated emulsions, redispersing, digesting and either during or after digestion adding a powerful halogen acceptor, and usually an excess of bromide ions and a background stabilizer and coating the emulsion. Preferably the silver halides, e.g., silver chloride as in the case of US. Pat. 3,178,293, are precipitated in the presence of a plumbous ion and then suflicient soluble bromide is added to convert a substantial portion (approximately of the silver chloride to silver bromide. The emulsion is coagulated, washed and redispersed in the manner described in US. Pat. 2,772,165. A halogen acceptor, e.g., stannous ion, frequently as stannous chloride is added and the emulsion digested and after the addition of final adjuvants, e.g., hardener, buflers, etc,, the emulsion is coated. The water-permeable colloids in the listed patents can be used.

One of the difficulties with the above and similar systems which are photodevelopable is that they are adversely aifected by the relatively high level of ambient flare light which exists in the exposure region of the currently commercially available high intensity oscillographs. This is due to light scatter from the high intensity exposing lamps (mercury arc/xenon) employed in producing images of grid lines, timing lines and oscillographic trace information. This flare light tends to produce an over-all low level exposure of the emulsion layer both before and after the trace exposure. In addition to producing an undesired background density which reduces image contrast, this low level exposure, particularly when it occurs prior to the high intensity imaging exposure, can desensitize the emulsion to the subsequent imaging exposure resulting in high background density which is observed after wet processing and a loss of writing speed and/or loss of timing line trace density. In addition, where stannous chloride is used as the halogen acceptor it is necessary to use special liquid developers where it is desired to wet process the exposed elements.

SUMMARY OF THE INVENTION This invention pertains to an improved process for making colloid-siver halide emulsions for oscillograph recording elements which comprises:

(1) admixing silver nitrate with an acidified solution of a water-soluble chloride containing a water-permeable, macro-molecular organic colloid binding agent for the silver halide grains,

(2) ripening the precipitated emulsion for about 5 to about 50 minutes at about F. to 160 F.,

(3) mixing with dispersion 50-160 mole percent of a water-soluble bromide,

(4) setting the resulting emulsion and washing and redispersing it,

(5) digesting the redispersed emulsion for 5 to 30 minutes at to F. and prior to completion of digestion admixing a halogen acceptor;

characterized in that there is added to the digested emulsion from 80 to 240 mole percent of a Water-soluble chloride, all percentages being based on silver. An important point is that the soluble chloride salt be added after digestion and prior to coating. During the precipitation step 0.33 to 10 mole percent of a Water-soluble plumbous salt may be present per mole of silver.

The emulsion is coated on a suitable support. Emulsions made by the above process have several advantages over the silver halide emulsions of the prior art when used in high-intensity oscillographic recording instruments.

The precipitation can be accomplished by using any of the water-soluble silver salts and water-soluble halides described in the patents listed above, e.g., lithium, sodium, potassium, calcium, magnesium and ammonium, chloride, bromide and iodide listed in Hunt US. Pat. 3,183,088. The precipitation is preferably carried out as described in Bigelow US. Pat. 3,178,293 by admixing silver nitrate and a plumbous salt in aqueous solution with an aqueous acidified solution of the colloid and water-soluble halide. After precipitating and ripening, the emulsion is washed, preferably in the manner described in Moede U.S. Pat. 2,772,165. The emusion is redispersed and digested in the conventional manner. At this point or prior to completion of digestion, optical sensitizers may be added to increase the spectral response of the emulsion for use in instruments employing a variety of light sources. Gold salts and a small amount of an alkali metal thiocyanate may be added during digestion. A plumbous salt, e.g., plumbous nitrate or plumbous acetate may be aded as described in Hunt U.S. 3,033,682.

In the case of silver halide emulsions for photo-developable direct writing elements which require the presence of a halogen acceptor, suitable compounds comprise stannous chloride, salts providing iodide and thiocyanate ions, molecular iodine, alkali-metal nitrites, phenylenediamine, aminophenols, hydroquinones, 3-pyrazolidones and other known halogen acceptors such as those disclosed in U.S. Kitze 3,241,971; McBride 3,271,157; 3,207,136 and 3,287,137 and Fix 3,326,689. The optical sensitizing dyes of such patents may be used.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred halogen acceptors for this invention, where it is desired to use photodevelopable direct-writing emulsions which may be Wet-processed, are alkali-metal and ammonium iodides and thiocyanates. In general, from .03 to 2.0 mole percent based on the silver halide present in the emulsion of the above iodides or thiocyanates may be used. The silver halide emulsions of this invention are preferably of the silver halide emulsions of this invention are preferably of the silver bromide or silver chlorobromide type although a silver iodobromide can also be used. While there are many useful soluble chloride salts, those which are readily available and least expensive are preferred, e.g., alkali metal and amonium chlorides. The preferred quantity is approximately 160 mole percent of chloride ion based on the silver halide. The viscosity of the emulsion may be adjusted by the addition of gelatin and/or other coloid. In general, the ratio of coloid to silver halide is 2:1 although this is not at all critical. The emulsions are coated to give a dry coating weight equivalent to about 30 mg. AgBr/dmfi.

In order to more specifically illustrate the features of this invention, the following examples are set forth below. They are not intended to limit the scope of the invention except as set forth in the claims.

EXAMPLE I A gelatino-silver chlorobromide emulsion was made by slowly adding an aqueous solution containing a mixture of 0.15 mole of silver nitrate and 0.005 mole of plumbous nitrate to a gelatin solution containing 0.15 mole of potassium chloride and acidified with 0.005 mole of hydrochloric acid. The precipitation was carried out under Wratten Series 1 red safelight manufactured by the Eastman Kodak Company. The temperature at precipitation and for 40 minutes thereafter was held at 140 F. After sium bromide was added while the mixture was held at 140 F. the resulting emulsion was coagulated, washed and redispersed in a manner similar to that described in Moede U.S. Pat. 2,772, 165. To the redispersed silver chlorobromide emulsion there was added 25 grams of inert gelatin and the emulsion was digested in the presence of 0.006 mole of potassium thiocyanate and 4.6 10 mole of auric chloride for 40 minutes at 140 F. After digestion, the emulsion was divided into 8 portions and halide ions in the form of potassium chloride, potassium bromide and potassium iodide were added to the various portions as indicated in the table below. Final adjuvants, e.g., hardeners, Wetting agents, etc., were added and the layers were coated on paper supports in an amount of approximately 30 mg./dm. (expressed as AgBr). The coatings were dried in a conventional manner.

To determine the sensitometric characteristics of the material it was exposed through a power of 2 step wedge in an electronic flash sensitometeer, Edgerton, Germeshausen and Grier Mark VI, using a Xenon flash tube at sec. After photodevelopment, which was performed by exposure to black light fluorescent tube for 4 minutes at 50 meter candles intensity, the sensitometric speed is expressed as the number of steps visible. The maximum densities obtainable and the background densities were measured with a reflection densitometer (Mabeth Quanta Log Densitometer Model RD100 14). Chemical development was 1 minute at 68 F. in a developer having the following composition:

Grams N-methyl-p-aminophenol sulfate 1.5 Hydroquinone 6.0 Sodium sulfite (anhydrous) 19.5 Sodium carbonate (anhydrous) 28.0 Potassium bromide 0.8

Water to make 1.0 liter.

The developed strips were rinsed and then immersed for 5 minutes in a fixing solution having the following composition:

Grams Sodium thiosulfate 240 Sodium sulfite (anhydrous) 15 Acetic acid, 28% 47 Potassium aluminum sulfate 1.0

Water to make 1.0 liter.

The test strips were washed and dried and read on a densitometer as described above.

To determine the characteristics of photographic elements of this invention when used in commercial oscillographs, samples of test material were exposed in a normal manner in a commercial mercury arc oscillograph identified as Honeywell Viscorder Model 1612 at a transport speed of 0.4 inch per second. The exposed samples were developed, fixed, washed and dried and the densities read as described above. The emulsion sensitivity was measured by a visual comparison of the timing line trace densities.

The results of testing as described above are shown the ripening, an aqueous solution of 0.24 mole of potasin the following table.

TABLE I.OOMPARISON OF EFFECT OF EXCESS HALIDE ION Moles of soluble Sensitometry Wet processed halides/moles of Photolyzed Wet processed oscillogra-phic test silver halides Visible Visible B G. Timing Br- I- steps D-rnax. B.G. steps D-max. B.G. density lines 0 0 7 25 19 8 98 02 0'; Weak. 0 0 6 .20 14 10 1. 17 .01 04 Stung. 0 0 6 .19 .12 10 1.14 .01 .05 Do. 0. 8 0 7 12 .06 7 1.11 00 .21 None. 0 0. 01 8 43 19 7 1. l3 01 04 Weak. 0 0. 01 7 .45 20 7 1.15 .01 .05 Medium. 0 0.01 7 .40 .17 8 1.17 .01 .06 Strong.

Note that effect. of chloride ion is observed in absence of other halides (B) but it is preferred to include lodid e ion G) for effect on photolyzed response (halogen acceptor). Amounts of chloride above approx. 1.0 may he used but are not; necessary.

15. G. =Backgr0und density which is the dilicrcnce between white paper and developed sample.

EXAMPLE II Low levels of bromide combined with high chloride levels An emulsion was made as described in Example I and Rroduced.1.ngher W Speed while reitaming 10W flare two portions were treated to give an emulsion like (G) hght .sensltlvlty High levels of iq i m absence of in Example I, that is, there was added to the emulsions chlonde produces fl1re ScnS1t1v1tY- just prior to coatin 1.6 moles of chloride ion and 0.01 place of the gelatm bmdmg agent usfid m the fore mole of iodide ionfone portion was coated as such and going examples there can be substituted other natural or was used as a ControL To the other portion there was synthetic water-permeable organic colloid binding agents,

added the amount Shown in the following table of the including the binding agents listed in Hunt US. Pat.

optical sensitizing dye:

l0 Suitable supports for the novel photographic emulsions of this invention include those used in the prior art on oscillographic recording elements. The preferred support 5- 3-methyl-2-thiazolinylidene-isopropylidene 3-ethylrhodanine.

The results are shown below: is a photographic grade paper but may be a hydrophobic TABLE 11 Sensitornetry Wet processed Photolyzed Wet processed oseillographic test Visible Visible B.G. Timing Ctg. steps D-max. B.G. steps D-rnax. B.G. density lines H (like G above in Ex. 1) 7 .43 .20 8 1.11 .01 .08 Strong. I (like G plus 0.005 g. dye) 8 45 .24 10 1.17 .01 .10 Very strong.

N oTE.Optical sensitizing dyes increase speed.

film composed of a cellulose ester, e.g., cellulose acetate EXAMPLE In or a polymer, e.g., polyester films disclosed in Alles et 211., Two portions of the emulsion of Example I were pre- US. 2,627,088 and Alles US. 2,779,684.

pared, one of which was digested in the presence of Radiation-sensitive elements coated with the emulsions 4.6x l0 mole of auric chloride as a chemical sensitizer, made according to this invention show a significant reand potassium thiocyanate as described in Example I. duction in oscillographic flare light sensitivity when wet No auric chloride was added to the second portion of processed without loss of sensitivity to the oscillographic the emulsion which was otherwise treated similarly. Both trace thus providing a higher trace density and a cleaner portions contained 1.6 mole of chloride ion and 0.01 of background. There is also an increase in timing line iodide ion added just prior to coating. The results are density when wet processed which is believed to be due shown in the table. to reduced flare light desensitization. There is also a TABLE 111 Seiisitometry Wet processed Moles of soluble oscillograpliic halides/moles of Photolyzed Wet processed test silver halides Visible Visible B.G. Timing Ctg. Cl- Br- I- steps D-max. B.G. steps D-max. B.G. density lines 1 1.06 0 0.01 7 .52 .26 11 1.13 .00 .08 Strong.

Auric chloride digestion K 1.6 0 0 7 .44 .26 9 1.08 .01 .04 Do.

Like K, but no gold salt was present Chemical sensitization with a gold salt can be used to reduced background density when the exposed element increase chemically developed speed without loss of chlor is photodeveloped in ambient room lighting of lower ride effect on timing line response. Chemical sensitization intensity than the oscillographic image exposing intensity. is not necessary for the chloride effect. The emulsions prepared according to this invention also show improved aging stability. EXAMPLE V The embodiments of the invention in which an exclu- For portions of a silver halide emulsion were prepared sive property or privilege is claimed are defined as as in Example I and potassium chloride, bromide and iofollows: dide were added just before coating to provide halide ions 1. A process for preparing photographic silver bromide as indicated in the following table along with the sensiemulsions comprising tometric results. (1) admixing silver nitrate with an acidified solution TABLE lvfMlxTUREs OF HALIDES Moles of soluble Sensitometry Wet processed halides/moles oi oscillographic silver halides Photolyzed Wet processed test Visible Visible B.G. Timing Cl- Br- I- steps D-rnax. B.G. steps D-max. B.G. density lines 1.5 0 0. 01 7 .59 .31 7 1.27 .02 .02 Weak. 1.6 0.4 0.01 7 .56 .27 s 1.24 .03 .05 Strong. 1.6 0.8 0.01 7 .52 .26 10 1.26 .02 .06 Do. 0 0.8 0.01 e .32 .15 0 1.22 .00 .23 Do.

of a water-soluble chloride containing a water-permeable, macromolecular organic colloid binding agent for the silver halide grains,

(2) ripening the precipitated emulsion for about to about minutes at about F. to 160 F.,

(3) mixing with the dispersion 50-160 mole percent of a water-soluble bromide selected from the group consisting of lithium, sodium, potassium, calcium, magnesium and ammonium bromide,

(4) setting the resulting emulsion and washing and redispersing it,

(5) digesting the redispersed emulsion for 5 to 30 minutes at F. to 130 F. and prior to completion of digestion admixing a halogen acceptor;

characterized in that there is added to the digested emulsion from 80 to 240 mole percent of a water-soluble chloride, all percentages being based on silver.

2. A process according to claim 1 wherein prior to completion of digestion there is incorporated with the silver halide based on the silver at least one of the following constituents:

(a) up to mole percent of a water-soluble bromide and (1)) up to 5 mole percent of plumbous nitrate or acetate.

3. A process according to claim 1 wherein said binding agent embodies gelatin.

4. A process according to claim 1 wherein said watersoluble chloride is potassium chloride.

5. A process according to claim 1 wherein said halogen acceptor is potassium thiocyanate.

6. A process according to claim 1 wherein nitrate or acetate is present during precipitation of silver halide.

7. A process according to claim 1 whrein iodide ions are present from the halogen acceptor.

8. A process according to claim 1 wherein the emulsion contains an optical sensitizing dye.

References Cited UNITED STATES PATENTS 3,033,678 6/1962 Hunt 96-108X 3,178,292 4/1965 Fix 96-108 3,178,293 4/1965 Bigelow 96-108 3,183,088 5/1965 Hunt 9645.2 3,260,605 7/1966 Sutherns 96-108 NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner US. Cl. X.R. 96107, 109 

